Boom tube material and fastening

[Christian Lucas]

Hello Jim , John ,

in my eyes it is better to design a rigger that will break records for this competion and no other . A wave or any other debris that will hit the hull to give it the kick to take off is not the design we have to look for . This happen years ago at the tethered line boats when they ad spring and shockabsorber to the sponson to get a smoth ride but they set no new records .It's ok if you want to win a competion at a water you know befor that the lake has allways rough water condition . But for a record you select the starting time and look for a very silent moment on the lake to have a mirror like water . And for this moment the best streamlined boatdesign will be the best . So to streamline the booms and all other parts will allways lower the power your engine has to push the boat to the limit. I think we have moore to think about the position of the booms and the sponsondesign . For me i will plaze the lift creating parts as close as possible to the c.g. or in a better position like Hans Lehner has done with his small record rigger . As the boats are somthing of a surface effect ship / plane we have to looke at some of the succsesfull,designs like the ekranoplane from Rushia . The use the aerostyle wing section to ad lift when they start out of the water . And you need a very big tailwing to get the boat stabilised when the bad unknowen wave ,turttle or gost will kick the sponson off.

But if this will happen a record is far away. Indycar are not designed to stay a big jump without a lift off . I only know when they run formula1 race at the old Nürburgring Northschleife there are some jumps where the cars fly a longer distance but this days are gone .

Have no pic of the Lehner rigger so this show the boat , http://www.hobbydirekt.de/WP-SX-4000-LEHNER-STRAIGHTWAY-Graupner-2000::130762.html

 

[John Finch]

Interesting boat Christian. When Kentley Porter and I set nitro oval records years ago we had a problem with the tail jumping up when we hit our launch wake even after two laps of waiting for it to flatten out. Andy Brown suggested adding tail feathers like on his heat racing hydros to prevent the jump. I tried it a couple years later when I lowered the 67 oval record and it worked.

 

[Jim Allen]

Christian,

I read somewhere that a bullet shaped nut behind the propeller would generate more drag than a short lock nut & shaft. What are your thoughts & experience with this? The mechanical design of the rudder setup would give the necessary rigidity to the rear of the boat & the rudder mounting bracket also. It would appear that the mounting design of the sponsons would make the entire boat a very rigid, non-twisting, assembly.

JA

 

[dwilfong]

Ridged boats , boom tubes and turn fins are not the best setup for heat racing for me. I made a .050 thick Ti turn fin for my SGX and it flexes a lot............

Tried to make a backer for it and the boat was way to unpredictable.

It blows most minds when thy see this fin on the boat and I can flex it almost 1" in either direction.

Thy can't believe how the boat handles with this fin.

If you grab the sponsons on my SGX you can twist them and the whole tub will also twist. You think this would make for a very unstable boat but to the contrary it helps the boat handle rough water better.

When you can go in to a corner and the inside sponson pops up so high you can see the bottom of the boat. then snaps right back down not losing a beat you know the set up is right.

I call it giving the fin.........................LOL

Had a few back away from the pond as it is coming out of turn 4...................

How dose that boat stay on the water????????????????..............Hear it at every race.................

Many different driving styles and boat set ups. every one has there favorite.

My self I like a boat that is not to twitchy or tight. Makes it easer for me to control.

Show me one racing or flying machine that is ridged.........................they all get bowed up and flap around......................if not thy break.................

 

[Charles Perdue]

Mr. David, then you should see the BOSS boats run and corner. Extremely rigid, extremely predictable running and turning in any racing water. I do not want a twitchy boat when I am running next to other boats or next to the bouys. I want to know where it is going..

For those of you that have never seen one run.......well, you should just see one run, right Marty????

And the BOSS setup is a complete system not just one or two things.

Charles

 

[dwilfong]

I am not the best drive I will tell you that............................

I need some cushion to make up for my bad driving................

Kind like a delayed reaction so I can keep up with it or it gets a head of me.........................

Now watching Stu drive his crap shooter or Tom drive his little red wagon RR it is a totally different set up as thy are a head of the boat............................................

Me ..I would be bouncing off all the boat and buoys......well more than I do now.....................LOL

Different setups for different drivers.....................

 

[Charles Perdue]

David, it sounds like our driving abilities are very similar.

That is why I did the BOSS design in the beginning, to try to maximize handling to offset my poor driving, and it helped. But when it is put in the hands of someone like Steve O'Donnell it becomes amazing.

Charles

 

[Christian Lucas]

Hi Jim ,

my way is to streamline all underwaterparts and a bullet shape propnut will give a good waterflow when i run a full submerged propeller . But with surface propellers there is so much turbolence and air watermix around that such sreamline will not help but also dosn't ad much drag . It's to small to play a big rule . I love to run propellers very high ,prophub obove watersurface is good and use ansmall ski or rectangular strut and it makes moore propnoise . But i am crazy so maybee it's wrong . My Swedish friends show me to use two drivedog for a propeller and this is what i like on riggers.

I will show you next i will test about propellerdesign ,it's realy strange but wy not . I life once .

 

[Jim Allen]

Christian,

I use a machined, one piece, hexagon shaped strut tube that is rounded on the bottom. The outside edges of the hex are left very sharp to keep the water from climbing up the sides. Propeller center lines are sometimes as high as 9/16" above the water's surface at speed. I'm not sure what problems the different size propeller hub diameters can create; maybe none.

 

[John Finch]

David,

The problem I have had with boom tubes that flex is that when you throw the boat into a turn the right sponson gets twisted when the turn fin grabs and that raises the AOA of the right sponson dramatically. Then the AOA of the turn fin lifts the right sponson. ( with a cupped fin) If you hold your boat by the tub and push outward on the turn fin you will see how the AOA changes dramatically. Maybe that is why your right sponson rides so high in the corners.

John

 

[dwilfong]

John think about what I said with the fin flexing ................................................................

In stead of trying to control the sponson let the fin act as a shock absorber.

When you push on my fin the sponson dose not move much at all the fin flexes.

 

[John Finch]

I guess the turn fin cushions the blow when it flexes so you have a combination that works?

 

[dwilfong]

all of Andy's eagles have a fin that flexes. Some like a backer on them to give them better control. My self I do not like the backer and I went father by using Ti witch dose react different than the SS and making the fin longer front to back.

It all depends on how you like your boat to drive.

Aluminum bends CF flexes till it breaks. you will change a whole lot of AL tubes from slight bends. CF you only change if it breaks.

The two tubes take different fin setups. You can't just put CF tubes on a boat not setup for them.

Ask any one who has tried.............................

I helped a buddy with his gas Rico rigger. It has Al tubes thy bend all the time as he is learning how to drive the boat. One buoy hit and thy are bent.

Will change it over to CF here soon and set the fin and boat up to make it work. Every one tells him not to do it. It will not run right.

Thy are right if you don't make other changes.

How much solid rod you put in the tubes will make a difference on how the boat works also.

I have a old SG I set up for a buddy. it runs a 1.01 I did in it. the old tubes are really small compared to the new SGX boats but it runs like a dream.

The only difference is it will not take much of a hit to break them.

As far as stability in running it likes the rough water better. Dose not pop of as much and those tubes flex................................

 

[Jim Allen]

Christian,

On the SX 4000, do the two side rails use end grain balsa between the carbon fiber pieces? I found some very good photos on the Offshore Electrics Forum. The very clever design of the rear edge of the sponsons is similar to those used on George Mirov's A-2 tether boat.

JA

 

[BobBonahoom]

I was thinking about the first post and remembered that the silicone self fusing tape I have been putting on my tuned pipes is also very strong and sticks really well. I put it on the pipes for thermal reasons, but I wonder how well it might work for holding sponsons on boom tubes? I did a quick google of "self fusing silicone tape" the the first one that came up claims tensile strength of 700 psi. This might just work. www.xtremetape.com

 

[Jim Allen]

I was thinking about the first post and remembered that the silicone self fusing tape I have been putting on my tuned pipes is also very strong and sticks really well. I put it on the pipes for thermal reasons, but I wonder how well it might work for holding sponsons on boom tubes? I did a quick google of "self fusing silicone tape" the the first one that came up claims tensile strength of 700 psi. This might just work. www.xtremetape.com

Bob,

It looks as though from the specs that it can stretch 300%. Even with the high tensile strength this probably would not be helpful, especially on the skid fin side. I use Scotch Bi- Directional Filament Tape # 8959, Extreme Tape for Extreme Applications. This tape is designed as a high performance specialty packaging tape, combines a strong polypropylene backing reinforced with continuous bi-directional glass yarn filaments and a synthetic rubber resin adhesive. This heavy-duty tape is specifically formulated to provide good adhesion to a wide variety of surfaces, including metal, plastic, and fiberboard. A multi-layer synthetic-rubber adhesive system prevents delamination while protecting the tape from shearing. With typical tensile strengths of 150 lb/inch longitudinal and 50 lb/inch width in cross direction, Scotch Bi-Directional Filament Tape 8959 is an ideal choice for high-strength box reinforcing, heavy-duty sealing, shipping, splicing, and palletizing.

Built for Strength

Scotch Bi-Directional Filament Tape 8959 is reinforced with continuous glass yarns in both the longitudinal and transverse direction along with a biaxially oriented polypropylene backing. It has a tensile strength of 150 lb/in, an adhesion to steel value of 100, and 6% elongation at break. The tape is 5.7 mil thick and a multi-level synthetic-rubber adhesive prevents delamination of fiberglass from backing. Brands, bar codes and other graphics can be read through the translucent tape.

Many Uses

Use fiberglass strapping tapes where strength is critical. It is ideal for securing loads and sealing packages for shipping and handling. Industrial and commercial users include manufacturers and distributors of food and beverages, sporting goods, piping, metal fabrications, automotive parts and furniture. Applications include box closing and sealing, packaging, holding, strapping and general bundling. Apply with a portable hand-held dispenser or stationary definite-length dispenser.

JA

 

[John Finch]

Bob,

Just bought some of the tape thinking it might work well on my electric boats where I add cap banks etc. Thanks,

John

 

[BobBonahoom]

I taped up a Zipp 12 boom rod to a telescoping brass tube with 2 layers of silicone self-fusing tape from Ace Hardware. This tape is specified as 950 psi tensile. I let it sit over night to make sure it was fused and then put the brass tube in the vise and tried to pull it apart. Just as Jim predicted, when I pulled on the boom rod, it stretched out about 1/8-1/4". No matter how hard I pulled I could not make it slip or stretch irreversibly. It always can back to the same spot when I stopped pulling. That made me wonder if it might be useful in creating "dynamic toe-in" on the turn fin sponson? In other words, toe-in only when turning. I know some boats like a little toe in on the right, but I was never sure why. Does anybody know the reason toe in works on some boats? Could dynamic toe-in be helpful?

 

[John Beardslee]

Anyone how has run a twin knows how helpful toe in can be. With two props wanting to take the hull right, either you have to add toe in the turn fin, add left rudder or add more pitch to the right prop, what ever it takes to get the hull running straight, they don't like turning left!!!!!!

Thanks, John

 

[dr gary turner]

Christian,

I use a machined, one piece, hexagon shaped strut tube that is rounded on the bottom. The outside edges of the hex are left very sharp to keep the water from climbing up the sides. Propeller center lines are sometimes as high as 9/16" above the water's surface at speed. I'm not sure what problems the different size propeller hub diameters can create; maybe none.